Henderson DUSEL Capstone Workshop Stony Brook University, New York May 4, 2006

1
Henderson DUSEL Capstone WorkshopStony Brook
University, New York May 4, 2006
Why Geologists Date Rocks Techniques and
Comparative Geochronology at Henderson DUSEL
Holly Stein OrePets Chair, HUSEP-Geoscience Ore
Geology, Magmatic-Hydrothermal Processes,
Petrogenesis AIRIE Program, Colorado State
University, USA
AIRIE-CSU
Stony Brook Capstone Workshop Meeting, May 4-7,
2006
2
My family has owned this land for generations,
and we aint never seen no ocean on our property
. . .

• Geologic Time Why is it important?
• Absolute time is our only means to correlate
  global events with certainty, continent-to-contine
  nt
• Absolute time is our only means to understand
  rates of geologic processes and geologic change

The present is the key to the past, and the past
is the key to the present . .
AIRIE-CSU
Stony Brook Capstone Workshop Meeting, May 4-7,
2006
3
AIRIE-CSU
Stony Brook Capstone Workshop Meeting, May 4-7,
2006
4
What do we learn from dating geologic materials?

• Globally, meteorite impacts, climatic changes,
  mass extinctions, sea level changes, periods of
  high volcanic activity, paleo-oceans and
  paleo-atmosphere, elemental cycling
• Locally, magmatic evolution in time and space,
  eruption cycles, metamorphism (thermal and
  deformation), cooling rates, sedimentation rates,
  uplift and erosion rates, metallogeneis

Geochronology lends enormous power for
interpreting geologic events and processes
AIRIE-CSU
Stony Brook Capstone Workshop Meeting, May 4-7,
2006
5
How do we date geologic materials?

• Radioactive decay parent isotope ? daughter
  isotope
• (known rate, half-life of parent isotope on the
  scale of age of the earth)
• U-Th-Pb (238U?206Pb, 235U?207Pb,
  232Th?208Pb) Silicates, Phosphates
• Rb-Sr (87Rb?87Sr) Silicates
• Sm-Nd (147Sm?143Nd) Silicates
• K-Ar (40K?40Ar) Silicates
• 40Ar/39Ar (40K?40Ar) Silicates
• Lu-Hf (176Lu?176Hf) Silicates,
  Phosphates
• Re-Os (187Re?187Os) Sulfides, Oxides,
  Organics

AIRIE-CSU
Stony Brook Capstone Workshop Meeting, May 4-7,
2006
6

• 184Os 0.02
• 186Os 1.60
• 187Os 1.51
• 188Os 13.3
• 189Os 16.2
• 190Os 26.4
• 192Os 41.0

• 185Re 37.398
• 187Re 62.602

Half-life t1/2 41.6 Ga ?187Re 1.666 x 10-11
yr-1 (Smoliar et al. 1996)
AIRIE-CSU
Stony Brook Capstone Workshop Meeting, May 4-7,
2006
7
m

( x )
y

b
187Os
t gt 0 (isochron)
188Os
t 0
arsenopyrite
magnetite
pyrite
chalcopyrite
187Re
188Os
AIRIE-CSU
Stony Brook Capstone Workshop Meeting, May 4-7,
2006
8
Re-Os data for magnetites and pyrites, Cala
Fe-Cu-Au mine, Spain
AIRIE, unpublished
for isochron plot
Cala Fe oxide mine
pyrite
Cambrian organic-rich carbonates
massive magnetite
AIRIE-CSU
Stony Brook Capstone Workshop Meeting, May 4-7,
2006
9
Frasnian-Famennian Boundary
Stein et al. 2006
AIRIE-CSU
Stony Brook Capstone Workshop Meeting, May 4-7,
2006
10
Molybdenite (MoS2) a special case

• Re present in parts per million (ppm)
• Nearly all Os is radiogenic daughter (ppb level
  187Os)
• measure 187Os and Re concentrations, solve for t
• 187Os 187Re (elt - 1)

1800 6 Ma 1801 6 Ma
1773 6 Ma 1773 6 Ma 1775 6 Ma
AIRIE-CSU
Stony Brook Capstone Workshop Meeting, May 4-7,
2006
11
Triton TIMS (Thermal Ionization Mass
Spectrometer) at AIRIE, Colorado State University
AIRIE-CSU
Stony Brook Capstone Workshop Meeting, May 4-7,
2006
12
What are we dating?

• In the lab
• We count isotopes, at high precision . . .
• In reality
• Isotopes reside in minerals . . .
• Minerals constitute rocks . . .
• Accuracy of age depends on what is analyzed . . .

Our understanding of the radiometric age is only
as good as our understanding of the rocks, and
their complete geologic history Knowledge of
geologic history determined from observations of
structures and textures at all scales
Geologic observations first, isotopic
measurements second
AIRIE-CSU
Stony Brook Capstone Workshop Meeting, May 4-7,
2006
13
Granite Porphyry
crowded porphyritic texture
phenocrysts
AIRIE-CSU
Stony Brook Capstone Workshop Meeting, May 4-7,
2006
14
phenocrysts
groundmass
1 cm
AIRIE-CSU
Stony Brook Capstone Workshop Meeting, May 4-7,
2006
15
Na-rich feldspar
quartz
quartz
biotite
K-feldspar
0.5 cm
AIRIE-CSU
Stony Brook Capstone Workshop Meeting, May 4-7,
2006
16
Granite Aplite
border phase, phenocryst-poor
few tiny phenocrysts
fresh rock
altered rock
quartz-magnetite molybdenite veinlets
AIRIE-CSU
Stony Brook Capstone Workshop Meeting, May 4-7,
2006
17
Granite Aplite
magnetite vein cuts quartz phenocryst
quartz-magnetite molybdenite stockwork veinlets
AIRIE-CSU
Stony Brook Capstone Workshop Meeting, May 4-7,
2006
18
Granite Aplite
magnetite vein cuts quartz phenocryst
ghost Na-rich feldspar phenocrysts in K-altered
rock
fresh biotite phenocrysts
K-feldspar stable
0.5 cm
AIRIE-CSU
Stony Brook Capstone Workshop Meeting, May 4-7,
2006
19
aplitic granite texture
telling relative geologic time
quartz-magnetite molybdenite veinlets
earlier veins
later veins
0.5 cm
AIRIE-CSU
Stony Brook Capstone Workshop Meeting, May 4-7,
2006
20
Some alteration types keep the rock strong
patch of remaining porphyry
quartz-magnetite alteration, veining and flooding
AIRIE-CSU
Stony Brook Capstone Workshop Meeting, May 4-7,
2006
21
Some alteration types keep the rock strong
quartz-molybdenite veining and silica flooding
AIRIE-CSU
Stony Brook Capstone Workshop Meeting, May 4-7,
2006
22
Molybdenite veining at intrusion margins
brain rock
toward melt

• Unique textures developed at fluid-silicate
  melt-crystallization boundaries

AIRIE-CSU
Stony Brook Capstone Workshop Meeting, May 4-7,
2006
23
melt substrate
deformed crystal mush

• Link experimental work to field reality to
  understand how granites crystallize and evolve
  metal-bearing fluids

AIRIE-CSU
Stony Brook Capstone Workshop Meeting, May 4-7,
2006
24
How do we date geologic materials?

• Radioactive decay parent isotope ? daughter
  isotope
• (known rate, half-life of parent isotope on the
  scale of age of the earth)
• U-Th-Pb (238U?206Pb, 235U?207Pb,
  232Th?208Pb) Silicates, Phosphates
• Rb-Sr (87Rb?87Sr) Silicates
• Sm-Nd (147Sm?143Nd) Silicates
• K-Ar (40K?40Ar) Silicates
• 40Ar/39Ar (40K?40Ar) Silicates
• Lu-Hf (176Lu?176Hf) Silicates,
  Phosphates
• Re-Os (187Re?187Os) Sulfides, Oxides,
  Organics

U-Pb dating viewed as the gold standard of
geochronology by many . . .
AIRIE-CSU
AIRIE-CSU
Stony Brook Capstone Workshop Meeting, May 4-7,
2006
25
Ireland and Williams 2003
U-Pb dating of zircon (ZrSiO4)
magmatic overgrowths, changing trace elements

• The mineral we dont see at the hand specimen
  scale
• The mineral that carries the majority of the U
  and Th budget (tens of ppm levels)

patchy recrystallization, resorption and
overgrowth

• Dating crystallization history of minerals and
  magmas
• Potential to date subsequent geologic events

AIRIE-CSU
Stony Brook Capstone Workshop Meeting, May 4-7,
2006
26
Cocherie et al. 2005
Monazite (CePO4)
A. Patchy single generation
B. Monazite intergrown with other phases
C. Zoned monazite with Th-rich margin
D. Patchy monazite crystal

• Monazite is easily annealed at about 200C,
  whereas zircon is annealed at about 450C
• Different minerals record different events

AIRIE-CSU
Stony Brook Capstone Workshop Meeting, May 4-7,
2006
27
Henderson and NSF

• The U.S. National Science Foundation has recently
  funded two research grants for work at the
  Henderson mine

Molybdenite 187Re-187Os dating
AIRIE-CSU
Stony Brook Capstone Workshop Meeting, May 4-7,
2006
28
Henderson and NSFGlobal SRM (Standard Reference
Material)
With the advent of Re-Os dating of molybdenite to
provide geologic time markers, there exists an
urgent and global need for a molybdenite standard
for interlaboratory comparison and calibration .
. .
AIRIE-CSU
Stony Brook Capstone Workshop Meeting, May 4-7,
2006
29
Henderson and NSFGlobal SRM (Standard Reference
Material)
A bulk sample of Henderson molybdenite from the
Henderson mill will become the global standard
for all laboratories engaged in Re-Os dating . .
.
AIRIE-CSU
Stony Brook Capstone Workshop Meeting, May 4-7,
2006
30
Henderson and NSFGlobal SRM (Standard Reference
Material)
The Henderson standard will be marketed by NIST
(National Institute of Standards and Technology)
as a SRM (Standard Reference Material)
AIRIE-CSU
Stony Brook Capstone Workshop Meeting, May 4-7,
2006
31
NIST-bottled samples of Henderson molybdenite for
Re-Os analyses at AIRIE-Colorado State University
and University of Alberta
AIRIE-CSU
Stony Brook Capstone Workshop Meeting, May 4-7,
2006
32
How long does it take to construct a major
porphyry style ore deposit?
Henderson and NSFTiming and duration of ore
formation
Answer 0.1 to 1 Ma (generally 100,000 to
500,000 years)
How long between pulses of stockwork vein
mineralization?
Answer A few thousand years, broadly comparable
to the eruption cycles for silicic volcanism
AIRIE-CSU
Stony Brook Capstone Workshop Meeting, May 4-7,
2006
33
Henderson and NSFTiming and duration of ore
formation

• Mutually beneficial industry academia
  partnership
• benefiting the greater scientific community
• raising our understanding of how ore deposits
  form
• improved models for mineral exploration

AIRIE-CSU
Stony Brook Capstone Workshop Meeting, May 4-7,
2006
34
Time-lapse photography of magma emplacement
Industry-based research

• Climax Molybdenum Company team of geologists
  (including Jim Shannon and myself) worked out the
  relative chronology of intrusions.
• What were the rates of magma emplacement?
• How are magmatic events linked temporally to
  ore-forming events?
• How long were these processes active?
• What terminated mineralization?

AIRIE-CSU
Stony Brook Capstone Workshop Meeting, May 4-7,
2006
35
For a DUSEL at Henderson high-precision zircon
ages for intrusive events can be linked
to high-precision molybdenite ages for
ore-forming events
Seedorff and Einaudi 2004
Five dimensions, three in space, time, temperature
AIRIE-CSU
Stony Brook Capstone Workshop Meeting, May 4-7,
2006
36
Henderson Primos Porphyry
Molybdenite (MoS2)
Quartz veins
AIRIE-CSU
Stony Brook Capstone Workshop Meeting, May 4-7,
2006
37
Re-Os data for Urad-Henderson molybdenites
AIRIE-CSU
Stony Brook Capstone Workshop Meeting, May 4-7,
2006
38
NIST SRM Henderson
younger
older
AIRIE-CSU
Stony Brook Capstone Workshop Meeting, May 4-7,
2006
39
A Henderson DUSEL for Geochronologists

• Cross deposit drifts, caverns, and drill cutouts
  to obtain oriented core
• Looking at the underside of an ore body under
  pristine conditions
• Time frames for emplacement of intrusions
• Link mineralization events to causative
  intrusions
• Isotopic changes in the system with depth (change
  in source)
• Intercalibrate Re-Os, U-Pb and other chronometers
• Determine cooling and uplift rate for northern
  Colorado Rockies
• Complete 3-dimensional reconstruction of geologic
  events in a time-temperature framework
• Understanding the deposit enables exploration
  models

AIRIE-CSU
Stony Brook Capstone Workshop Meeting, May 4-7,
2006